Monofilaments



ilnited States 3,057,040 MONUFILAMENTS John Anthony Cucuio, Wilmington, DeL. assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed June 18, 1959, Ser. No. 821,108 5 Claims. (CI. 28-82) This invention relates to novel nylon monofilaments and more particularly to a polycaprolactam monofilament which possesses a unique balance of properties and is particularly suitable for use as a fish line.

The tensile strength of an extruded filament of a thermoplastic such as polyhexamethyleneadipamide and polyeaprolactam may be increased by drawing the filament after extrusion. Drawing operations are frequently classed as hot or cold drawing, depending upon the relative temperature of the filament during the drawing operation. Any drawing operation at a temperature below the softening point of the filament yields a tenacious, stiff filament because the increase in tensile strength and reduction in elongation necessarily results in increased ,stifiness of the material. In applications for a filament such as its use in fabrics and for tire cord high tensile strength and high stifiness are desirable; however, this combination of properties of the monofilaments is undesirable when the material is to be used for fish line and like applications. The requirements for the latter application are high tensile strength, low elongation, and low stiffness and can only be obtained by a unique balancing of the composition and manner of preparation of the filament. An object of this invention is to provide a unique monofilament of high tensile strength, low elongation, and low stiffness. Another object of this invention is to provide a monofilament which has specific additives that enhance the desirable properties of the filament beyond those of the filament without such additives. Still another object is to provide a process for the preparation of the filament of this invention. These and other objects will appear hereinafter.

The above objects are accomplished by drawing in two stages an unextracted polycaprolactam monofilament containing approximately by weight of a plasticizer. The filament is drawn in water at a draw ratio of 4.3/1 at a temperature of 55 C. in the first stage, and in oil at a draw ratio of approximately 1.2/1 at a temperature of 150- 165 C. in the second stage. The resulting filament has a diameter of 3 to 30 mils with a desirable tensile strength and beam stitfness. The tensile strength bears a substantially linear relationship to diameter, or caliper, such that at a caliper of 3 mils the filament has a tensile strength of at least 110,000 p.s.i., and at 30 mils has a tensile strength of at least 73,000 with a beam stiffness over the above range of 150,000 to 230,000 p.s.i. In addition to the drawing operation and the plasticizer in the initial polymer, certain additives such as copper stearate in the amount of 0.01% to 0.1% by weight may be incorpor'ated in the polymer to enhance the knot strength of the filament. A pigment consisting of the oxides of copper, manganese and chromium may also be incorporated into the polymer or placed on the surface of the filament to impart weatherability to the filament, and to camouflage the filament in the water when it is used as a fish line.

Of the numerous drawing processes which are shown in the prior art, practically all result in the production of a somewhat stiff filament which is undesirable for use as a fish line. The filament of this invention is unique in that the filament strength exceeds that of known filaments at any given caliper, but, at the same time, exhibits a lower stifiness than is associated with filaments which have been drawn by known methods. The elongation of the filament of this invention is less than would be expected from its high tensile strength, thus providing the angler with better control.

Unlike improvements made to other types of equipment, the precise balance of properties in the filament of this invention are not readily apparent with simple visual inspection, but may readily be measured by laboratory techniques as set forth below. The measurements, and the formulas using these measurements, for defining beam stiffness, tensile strength, and breakload are given below. A comparison of the filament of this invention with those of the prior art may be made by comparing these quantities for two lines to determine the filament which possesses the lower apparent stiffness at substantially equivalent filament strengths. (1) Tensile strength (T.S.) in p.s.i.=%

(2) Beam stiffness (B.S.) in p.s.i.=%

Formula 1 above gives the tensile strength (T.S.) for a filament having a diameter (D) in inches and using the cross-sectional area and the break load (B.L.-) in pounds as measured on an Instron Universal Tensile Tester using a 10-inch gap (filament segment) and drawing at 10 inches per minute in an atmosphere at 23 C. and 50% relative humidity. Formula 2 gives the beam stillness (B.S.) of a line having a diameter (D) in inches. The beam stiflness is measured by attaching a weight of W grams to the center of a filament suspended between two supports spaced one inch apart, and by" measuring the deflection (d) in cms. which the weight has caused the filament to sag from the horizontal. This measurement is made in an atmosphere of air at 23 C. and 50% relative humidity after the weight has been on the filament for 30 seconds.

Two filaments (A) and (B) may be compared by taking two lines of equal breakload and comparing. Equa tion 1 for each filament, which by simple mathematics reduces to:

( Sa a b b By definition, the etfectiv stifiness of a filamentis the reciprocal of the deflection, and the effective stifine'ss may be expressed in terins of beam stiffness from Equa= tion 2:

B D (4) -0.00237W The ratio of efiective stiffnesses of two filaments to be compared may be seen to be a ratio of Equation 4 for Efi'ective stiffness (E.S.)

Comparative stifiness:

Example I The polycaprolactam used in this example had an inherent viscosity (I.V.) of 1.3 as measured at 0.5% by weight in a solution of m-eresol at 25 C., calculated according to the formula set fiorth in column 4 of United States Patent 2,895,948, issued on July 21, 1959, to' K. C. Brinker et al., and a monomer content of about 10% by weight of the polymer. This unextracted polymer flake was dried and thereafter extruded in a standard 1" extruder manufactured by the National Rubber Machine Company using a barrel temperature of 260 C. and a die temperature of 250 C. at a rate of /2% pound per hour. The strand was immediately quenched in water at about 7 C. for 1-2 seconds and led to a standard 3- roll, 2-stage, drawing apparatus using a common set of central draw rolls. The first stage draw was eifected in water at 55 C. at a draw ratio of 4.3/1 (ratio=final length over original length) and the second draw was effected in silicone oil at 160 C. at a draw ratio of 1.2/1. The drawn filament (approximately ll2 mils in diameter) was then wiped to remove the oil clinging thereto and wound at moderate tension on a suitable spool. The following properties are average properties exhibited by The knot strength was measured by tying the given knot in the filament, pulling the knot tight, suspending the knot equidistant from the clamps in the Instron Universal Tensile Tester, and following the procedure described hereinabove for determination of the tensile strength. The properties of this filament indicate that it would be outstanding for use as a fish line.

Other oils such as Ucon 50HB-280X (a polyalkylene glycol oil sold by Union Carbide Corp.) which do not degrade the polymer have been found to be operable in the second stage draw in place of the silicone oil described above. Other plasticizers which are operable in this invention include the cyclic lactams of the general formula EZi j II I o H where x is a positive integer of 4, 5, or 6. Additional experiments have indicated that the desired range of plasticizer concentration is 3%15% by weight of the polymer.

Example II To the starting polymer of Example I was added sufficient Ferro Black F-1335 to reach a concentration of 0.1% by weight of the polymer by tumbling the pigment and a binder with the polymer for about one hour before extruding the filament as described in Example I. F erro Black F4335 is a pigment containing a mixture of the oxides of chromium, copper, and manganese, and is sold by the Ferro Corporation. Several calipers of filament were extruded and the properties of this filament (shown below as S) were compared with three known commercial filaments, designated as A, B, and C. The formula as set forth hereinabove for comparative stiffness was used for the comparison of the filaments and the averages of the test data are given below.

Sug- Elonga- Caliper gested Tensile tion Beam Compar- Brand (mils) Load Strength (Percent Stifiness ative (lbs.) 0 Stiffness Length) Brand A was an uncolored resin and Brands B and C were tinted. When the line of this invention was placed in a standard U.V. Weatherometer with Brand A it was discovered that the instant filament possessed better proper-ties after 1000 hours of exposure than Brand A possessed after only 250 hours of exposure. This result and the results from the above comparison indicate that the filament of this invention is vastly superior to those of the prior art. With the exception of weatherability, the unmodified filament of Example I has properties similar to the six pound filament of this example. The slight decrease in tensile strength of the filament of this example as compared to the unmodified filament of Example I may be due to the pigment and binder placed in the polymer of this example. The low elongation of the filament of this invention makes the filament especially suitable for use as a fish line.

A number of determinations of tensile strength indicate the general ranges of tensile strengths of the filament of this invention are from 106,000 p.s.i. to 130,000 p.s.i. at a caliper of 6 mils and 80,000 p.s.i. to 104,000 p.s.i. at a caliper of 25 mils although some filaments have been produced which fall above this range. The range of beam stiffness for numerous filaments was found to be from 150,000 to 230,000 p.s.i. for filaments in the above caliper range. The properties of beam stiffness of the pigmented filaments of this example are comparable to the unmodified filament of Example I. The amount of pigment may vary from 0.05% to 0.25% by weight of the filament. 'The composition and amount of pigment employed should be such that sufiicient weather-ability and color (light gray) may be imparted to the filament at pigment concentrations low enough so that the strength of the line is not adversely affected.

Example III Percent Over- Beam Clinch Tensile Elongahand Stiflness, Knot, Strength tion Knot, p.s.i. p.s.i.

p.s.i.

The additive improved the tensile strength approximately 3.5% and the overhand knot strength approximately 25% over the same properties of the line of Example I with no noticeable impairment of the limpness or of the elongation of the filament. Experiments such as the above indicate that the acceptable and preferred range of concentration of the copper stearate is 0.01% to 0.1% by weight of the polymer. Other additives are also operable to further improve the properties of the instant line and are discussed hereinbelow. Similar improvements were obtained by adding 0.05 of copper stearate to the pigmented filament of Example II. In this case the copper stearate was first added to the polymer flake, which was then tumbled for one hour, and then the pigment was added and the tumbling continued for an additional hour, followed by extrusion and workup.

The above examples indicate that the filament of this invention is superior to those of the prior art and possesses the majority of properties which are desirable for its application as a fishing line. The filament of this invention should find other uses which require similar properties. Although the caliper of the filaments shown in the examples varies from about 8.7 mils to 20.4 mils,

the useful range of filament calipers in this invention is from 3 mils to about 30 mils.

The weatherability of this filament is markedly increased by the addition of the pigment specified above as evidenced by the fact that the line of this invention after 1000 hours exposure in a Weatherometer possessed qualities comparable to a known material (Brand A of Example II) after only 250 hours. Pigments of like characteristics are also within the purview of this invention.

The exact nature of the action of the copper stearate on properties of the filament is not shown. It is believed that the copper stearate acts both as a lubricant and a stabilizer for the filament. (Other lubricants which are operable include zinc stearate, Waxes, salts of organic fatty acids, and low molecular weight amides of organic fatty acids. Other stabilizers which are operable include other copper compounds, such as cupric chloride; aromatic amines; and phenolic antioxidants. Generally the copper stearate increases the strength of the filament as evidenced by the increase in overhand knot strength of 25% with a somewhat smaller increase in tensile strength (3.5%).

The preferred drawing process is a two-stage process as set forth in Example I. .A single-stage draw may be employed, but with somewhat inferior results with respect to the tensile strength of the filament. The single-stage draw yields a filament with increased transverse stability as shown by an increase of 18% in the overhand knot strength, but is not preferred since the more important property of tensile strength decreases about 5%.

The polycaprolactam is extruded as a filament at a temperature of 240260 C., desirably at 250 C., and is solidified by quenching. After quenching the extruded filament in a quench bath at about 525 C., the first stage of drawing is conveniently accomplished in water at a temperature of about 30 -55 C. and at a draw ratio of about 4.2 to 4.5. It is not critical that water be used as a drawing medium since other inert liquids such as trichloroethylene may be used. The second stage of drawing is accomplished in an oil, e.g. silicone oil, at a temper-ature of 150165 C. and a draw ratio of about 1.15 to 1.25. This provides a range of overall draw ratio of about 4.8 to 5.6. It is preferred that the first stage draw the filament about 4.3 times and the second stage about 1.2 times for an overall draw ratio of about 5.2.

Additional process steps may be employed in the drawing operation without adversely affecting the filament properties. Such operations may include two-stage addition of materials to the base polymer before extrusion and mild steam treatment of the filament upon the final windup spool by passing the spool through a steam chamber to reduce the strain in the filament.

By virtue of the greatly enhanced properties of the monofilament of this invention, its principal use is as a fishing line for bait casting, fly casting, trolling, surf fishing, and in other methods of fishing with a line.

.1 claim:

1. A monofilament of polycaprolactam in filament calipers of 3-30 mils having the dual characteristics of low beam stiffness and high tensile strength; said beam stiffness being in the range of 150,000 to 230,000 pounds per square inch; said tensile strength having a substantially linear relationship to filament caliper and being at least 110,000 pounds per square inch at a filament caliper of 3 mils and at least 73,000 pounds per square inch at a filament caliper of 30 mils.

2. A monofilament of polycaprolactam containing from 3-15% of weight of a plasticizer in filament calipers of 3-30 mils, and having the dual characteristics of low beam stiffness and high tensile strength; said beam stiffness being in the range of 150,000 to 230,000 pounds per square inch; said tensile strength having a substantially linear relationship to filament caliper and being at least 110,000 pounds per square inch at a filament caliper of 3 mils and at least 73,000 pounds per square inch at a filament caliper of 30 mils.

3. A monofilament as set forth in claim 2, which contains 0.05% by weight of copper stearate.

'4. A monofilament fish line of polycaprolactam containing from 3-15% by weight of a plasticizer, 0.01% to 0.1% 'by weight of copper stearate, and 0.05 to 0.25% by weight of an inorganic pigment containing the oxides of chromium, copper, and manganese, in filament calipers of 3 to 30 mils, and having the dual characteristics of low beam stiffness and high tensile strength; said beam stiffness being in the range of 150,000 to 230,000 pounds per square inch; said tensile strength having a substantially linear relationship to filament caliper and being at least 110,000 pounds per square inch at filament caliper of 3 mils and at least 73,000 pounds per square inch at a filament caliper of 30 mils.

5. -A monofilament fish line, 3 to 30 mils in diameter, and comprising unextracted polycaprolactam containing 0.1% by weight of the polymer of an inorganic pigment containing the oxides of copper, manganese, and chromium, and having the dual characteristics of low beam stiffness and high tensile strength; said beam stiffness being in the range of 150,000-230,000 pounds per square inch; said tensile strength having a substantially linear relationship to filament diameter and being at least 110,000

pounds per square inch at a filament diameter of 3 mils and at least 73,000 pounds per square inch at a filament diameter of 30 mils.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Man Made Fiber Table, Textile World Magazine, McGraw-Hill Publishing Co. (New York, N.Y.), 1957 revision relied on. (Copies available in Scientific Library and Div. 21.) 

1. A MONOFILAMENT OF POLYCAPROLACTAM IN FILAMENT CALIPERS OF 3-30 MILS HAVING THE DUAL CHARACTERISTICS OF LOW BEAN STIFFNESS AND HIGH TENSILE STRENGTH; BEAM STIFFNESS BEING IN THE RANGE OF 150,000 TO 230,000 POUNDS PER SQUARE INCH; SAID TENSILE STRENGTH HAING A SUBSTANTIALLY LINEAR RELATIONSHIP TO FILAMENT CALIPER AND BEING AT LEAST 110,000 POUND PER SQUARE INCH AT A FILAMENT CALIPER OF 3 MILS AND AT LEAST 738000 POUNDS PER SQUARE INCH AT A FILAMENT CALIPER OF 30 MILS. 